Electron-based crystalline undulator

We discuss the features of a crystalline undulator of the novel type based on the effect of a planar channeling of ultra-relativistic electrons in a periodically bent crystals. It is demonstrated that an electron-based undulator is feasible in the tens of GeV range of the beam energies, which is noticeably higher than the energy interval allowed in a positron-based undulator. Numerical analysis of the main parameters of the undulator as well as the characteristics of the emitted undulator radiation is carried out for 20 and 50 GeV electrons channeling in diamond and silicon crystals along the (111) crystallographic planes.Comment: 16 pages, 8 figures, Latex, IOP styl

Strong dependence of multiphoton detachment rates on the asymptotic behaviour of the ground-state wave function

Two-photon detachment from the F-minus negative ion is investigated within the lowest order of perturbation theory. We show that in accordance with the adiabatic theory a proper asymptotic behaviour of the 2p bound state wave function is crucial for obtaining correct absolute values of the multiphoton detachment cross sections. We find that the latter are substantially higher than it was previously believed.Comment: Latex IOP stile, plus 3 figures in PostScript file

Study of the features of masticatory efficiency in patients with acute cerebrovascular disorder by hemitype

The attention of dental researchers is constantly focused on assessing the quality of treatment for various pathologies of the dentоalveolar system, determining disorders of occlusal correlations, treatment, and prevention of diseases of the temporomandibular joint and periodontal tissue pathology. Numerous studies on the above aspects contain information on the characteristics of masticatory efficiency as one of the most vivid markers of orthopedic treatment, as it allows dentists to determine the quality of actual masticatory performance.The issues of functional diagnostics at the stages of rehabilitation of patients with partial defects of the dentition remain relevant, and therefore, the indicators of masticatory efficiency in prosthetics with removable dentures will be one of the most important criteria for adaptation to them. The situation exacerbates when such patients suffer from somatic pathologies of a neurological nature, in particular, acute cerebrovascular disorder.The aim of the research was to study the features of masticatory function in patients with a complicated course of acute cerebrovascular disorder with the neurological deficit by hemitypeThe study involved 25 people with a complicated course of acute cerebrovascular disorder with the neurological deficit by hemitype and 20 people from the control group, aged from 40 to 65 years, for whom partial removable laminar dentures with acrylic base and retaining bent metal clasps were manufactured according to clinical indications. All patients gave their free and informed consent to participate in the study.The masticatory efficiency was determined using the author's method based on the principle of graphical analysis of fragments of the agar-agar masticatory sample with subsequent programmed calculation and computer processing of numerical data.The evaluation indicators were as follows: the total number of fragments of the chewing sample and the number of fragments with a fraction of 500-1000 pixel2.Statistical analysis of the results was conducted using the Statistica 10.0 software package for Windows, and it embraced the following:1. Assessing the distribution of values and their correspondence to the normal one in the population.2. Comparison of the results obtained before applying a removable dental prosthesis and 30 days after its application.3. Intergroup comparison of the results.Thus, we observed an increase in the chewing sample parameters in the period from the beginning of orthopedic treatment until the 30th day of observation after applying a partial removable laminar denture. Despite the general trend, in the group of patients with ACVD, the masticatory efficiency was lower than that of the control group, which is confirmed by the difference between the total number of fragments (<17.22) and the number of fragments with a caliber of 500 to 1000 pixel2 (<4.41). In our opinion, this is due to the peculiarities of adaptation processes in patients with ACVD, who present with a much longer period than patients without a somatic pathology.The study revealed that the masticatory efficiency, restored by prosthetics with removable laminar dentures in the group of patients with a complicated course of ACVD by hemitype, one month after treatment is at the level of 88.68 (total number of fragments of the chewing sample) and 17.04 (number of fragments with a caliber of 500-1000 pixel2), which is a relatively worse indicator as compared to the control group. Thus, the total period of orthopedic rehabilitation for patients with ACVD is longer

Two-photon detachment of electrons from halogen negative ions

Absolute two-photon detachment cross sections and photoelectron angular distribution are calculated for halogen negative ions within lowest-order perturbation theory. The Dyson equation method is used to obtain the outer np ground-state wave functions with proper asymptotic behavior exp (-k r), corresponding to correct (experimental) binding energies E=k^2/2. The latter is crucial for obtaining correct absolute values of the multiphoton cross sections (Gribakin and Kuchiev 1997 Phys. Rev.A55 3760). Comparisons with previous calculations and experimental data are performed.Comment: Latex, IOP stile, 22 pages, 8 figure

Three-photon detachment of electrons from the fluorine negative ion

Absolute three-photon detachment cross sections are calculated for the fluorine negative ion within the lowest-order perturbation theory. The Dyson equation of the atomic many-body theory is used to obtain the ground-state 2p wavefunction with correct asymptotic behaviour, corresponding to the true (experimental) binding energy. We show that in accordance with the adiabatic theory (Gribakin and Kuchiev 1997 {Phys. Rev. A} {\bf 55} 3760) this is crucial for obtaining absolute values of the multiphoton cross sections. Comparisons with other calculations and experimental data are presented.Comment: 10 pages, two figures, Latex, IOP styl

Coherent radiation of an ultra-relativistic charged particle channeled in a periodically bent crystal

We suggest a new type of the undulator radiation which is generated by an ultra-relativistic particle channeled along a periodically bent crystallographic plane or axis. The electromagnetic radiation arises mainly due to the bending of the particle's trajectory, which follows the shape of the channel. The parameters of this undulator, which totally define the spectrum and the angular distribution of the radiation (both spontaneous and stimulated), depend on the type of the crystal and the crystallographic plane (axis), on the type of a projectile and its energy, and on the shape of the bent channel, and, thus, can be varied significantly by varying these characteristics. As an example, we consider the acoustically induced radiation (AIR) which is generated by ultra-relativistic particles channeled in a crystal which is bent by a transverse acoustic wave. The AIR mechanism allows to make the undulator with the main parameters varying in wide ranges, which are inaccessible in the undulators based on the motion of particles in the periodic magnetic fields and also in the field of the laser radiation. The intensity of AIR can be easily made larger than the intensity of the radiation in a linear crystal and can be varied in a wide range by varying the frequency and the amplitude of the acoustic wave in the crystal. A possibility to generate stimulated emission of high-energy photons (in keV - MeV region) is also discussed.Comment: published in J. Phys. G: Nucl. Part. Phys. 24 (1998) L45-L53, http://www.iop.or

Prospects for detection of detached double white dwarf binaries with Gaia, LSST and LISA

Double white dwarf (DWD) binaries are expected to be very common in the Milky Way, but their intrinsic faintness challenges the detection of these systems. Currently, only a few tens of detached DWDs are know. Such systems offer the best chance of extracting the physical properties that would allow us to address a wealth of outstanding questions ranging from the nature of white dwarfs, over stellar and binary evolution to mapping the Galaxy. In this paper we explore the prospects for detections of ultra-compact (with binary separations of a few solar radii or less) detached DWDs in: 1) optical radiation with Gaia and the LSST and 2) gravitational wave radiation with LISA. We show that Gaia, LSST and LISA have the potential to detect respectively around a few hundreds, a thousand, and 25 thousand DWD systems. Moreover, Gaia and LSST data will extend by respectively a factor of two and seven the guaranteed sample of binaries detected in electromagnetic and gravitational wave radiation, opening the era of multi-messenger astronomy for these sources.Comment: submitted to MNRA

Total spectrum of photon emission by an ultra-relativistic positron channeling in a periodically bent crystal

We present the results of numerical calculations of the channelling and undulator radiation generated by an ultra-relativistic positron channelling along a crystal plane, which is periodically bent. The bending might be due either to the propagation of a transverse acoustic wave through the crystal, or due to the static strain as it occurs in superlattices. The periodically bent crystal serves as an undulator. We investigate the dependence of the intensities of both the ordinary channelling and the undulator radiations on the parameters of the periodically bent channel with simultaneous account for the dechannelling effect of the positrons. We demonstrate that there is a range of parameters in which the undulator radiation dominates over the channelling one and the characteristic frequencies of both types of radiation are well separated. This result is important, because the undulator radiation can be used to create a tunable source of X-ray and gamma-radiation.Comment: published in J. Phys. G: Nucl. Part. Phys. 26 (2000) L87-L95, http://www.iop.org ; 12 pages, 4 figures, LaTe