The form factor of a hollow electron beam for transition radiation has been calculated. It has been shown that the characteristics of coherent radiation are significantly different for conventional ...solid and hollow beams. Numerical estimates have been obtained for terahertz radiation frequencies and relativistic energies of el-ectrons.
Smith-Purcell effect is well known as a source of monochromatic electromagnetic radiation. In this paper we present the generalized theory of Smith-Purcell radiation from periodic beams. The ...form-factors describing both coherent and incoherent regimes of radiation are calculated. The radiation characteristics are investigated in two practically important frequency ranges, THz and X-ray, for two modulation profiles, most frequently used in practice - a train of microbunches and a Gaussian-shaped one, characterized by sinusoidal modulation with an arbitrary modulation depth. On the base of the theory developed we show that a modulated electron beam consisting of a set of bunches makes it possible to improve significantly the spectral line monochromaticity of the light emitted, reaching values better than 1% for short gratings. We demonstrate as well that Smith-Purcell radiation can be used for non-destructive diagnostics of the depth of modulation for partially modulated beams. These findings not only open up a new way to manipulate the light emission using Smith-Purcell effect but also promise a profound impact for other radiation sources based on charged particle beams, such as undulator radiation in FELs, next-generation X-ray radiation source based on inverse Compton scattering, in a wide range from THz to X-rays.
In the theory of radiation emitted by bunches of charged particles, the effects of coherence are commonly taken into account by multiplying the intensity of radiation generated by a single particle ...by the form factor of the bunch, which depends on its size, shape, and particle distribution. Here, it is demonstrated that this approach is, generally speaking, incorrect for polarization radiation from a wide class of structures like photonic crystals and metasurfaces. The theory of coherent Smith–Purcell radiation from such structures has been developed. It is shown that the commonly accepted approach is applicable only under two conditions: (i) the observation point lies in the plane containing the trajectory of the bunch and the normal to the surface of the target, and (ii) the radius of the bunch is much smaller than the effective range of the Coulomb field of the moving electrons.
In this work, we construct for the first time the theory of small-angle transition radiation from multilayered structures. The theoretically obtained spectral and angular distributions of radiated ...photons are compared with those predicted by Geant4, a very popular package used today for numerical simulation of different physical processes. We demonstrate that, while spectral distributions ideally coincide, the angular ones differ. We argue that transition radiation from the multilayered structure must contain sharp spikes having the interference nature and caused by the effect of merging two maximum frequencies in dispersive media, and thus Geant4 needs improving in this respect. The transition radiation theory developed here for the small-angle case can play a vital part for the possible future Small Angle Spectrometer at the LHC, other experiments of this kind, and detectors for hadrons of the tera-electron-volt energy range.
It has been shown that polarization radiation of charged particle beams generally includes an incoherent form factor caused by a finite transverse size of a beam. Consequently, a widespread opinion ...that the form factor characterizes only coherent radiation of charge particle bunches is generally invalid. The reason for the existence of incoherent form factor is the interaction of charged particles with the target edge in the direction perpendicular to their trajectory. The incoherent form factor exists for diffraction radiation, Smith-Purcell radiation, and other types of polarization radiation in the case of transversely limited targets: transition radiation, parametric X-ray radiation, and Cherenkov radiation. It has been shown that the difference of the incoherent form factor from unity increases with a decrease in the ratio of the impact parameter to the transverse size of the bunch. Furthermore, it has been shown that the transverse part of the coherent form factor differs from unity to the same extent as the incoherent form factor.
An analysis of spectral-angular characteristics of diffraction radiation, both incoherent and coherent, has been performed. It is shown that radiation processes can be interpreted as Cherenkov ...radiation, which is produced by a region of dynamic polarization moving along a target edge with superluminal velocity vSL. Such radiation is generated if the condition vSL > c is fulfilled, which is the conventional 'threshold' Cherenkov condition.
The lack of tools to monitor the dynamics of (pseudo)hypohalous acids in live cells and tissues hinders a better understanding of inflammatory processes. Here we present a fluorescent genetically ...encoded biosensor, Hypocrates, for the visualization of (pseudo)hypohalous acids and their derivatives. Hypocrates consists of a circularly permuted yellow fluorescent protein integrated into the structure of the transcription repressor NemR from Escherichia coli. We show that Hypocrates is ratiometric, reversible, and responds to its analytes in the 10
M
s
range. Solving the Hypocrates X-ray structure provided insights into its sensing mechanism, allowing determination of the spatial organization in this circularly permuted fluorescent protein-based redox probe. We exemplify its applicability by imaging hypohalous stress in bacteria phagocytosed by primary neutrophils. Finally, we demonstrate that Hypocrates can be utilized in combination with HyPerRed for the simultaneous visualization of (pseudo)hypohalous acids and hydrogen peroxide dynamics in a zebrafish tail fin injury model.
mRNA was discovered in 1961, but it was not used as a vaccine until after three decades. Recently, the development of mRNA vaccine technology gained great impetus from the pursuit of vaccines against ...COVID-19. To improve the properties of RNA vaccines, and primarily their circulation time, self-amplifying mRNA and trans-amplifying mRNA were developed. A separate branch of mRNA technology is circular RNA vaccines, which were developed with the discovery of the possibility of translation on their protein matrix. Circular RNA has several advantages over mRNA vaccines and is considered a fairly promising platform, as is trans-amplifying mRNA. This review presents an overview of the mRNA platform and a critical discussion of the more modern self-amplifying mRNA, trans-amplifying mRNA, and circular RNA platforms created on its basis. Finally, the main features, advantages, and disadvantages of each of the presented mRNA platforms are discussed. This discussion will facilitate the decision-making process in selecting the most appropriate platform for creating RNA vaccines against cancer or viral diseases.
The study considers diffraction radiation, which is excited when an electron moves near a cluster of two interacting subwavelength particles. The interaction is manifested in the fact that the ...radiation field from each particle is determined not only by the external field of the electron, but also by the field of the neighboring particle. Based on the obtained expressions for the radiation field, the function of cluster polarizability is determined. It characterizes the cluster response to the field of the electron as a whole. It is interesting that the obtained response function of the cluster to an external field, even in the framework of linear theory, generally depends on the external field itself.
The safety of micro- and nanoparticle sorbents based on zero-valent iron and their detoxifying activity in peat eutrophic soil (Eutric Histosol) polluted by the emissions of a copper-nickel (Cu/Ni) ...plant in the Kola Peninsula are studied. Both iron nanoparticles and microparticles at a dose of 2% have emerged to be nontoxic according to the results of three standard bioassays based on the response of test organisms of different taxonomic affiliations. The toxicity is assessed according to the change in the root length of
Sinapis alba
L. seedlings in uncontaminated peat as well as the survival rate of the crustacean
Ceriodaphnia affinis
Lilljeborg and the protozoan
Paramecium caudatum
Ehrenberg in water extracts obtained of samples. Iron-containing preparations in a statistically significant manner reduce the ecotoxicity of soil caused by an extremely high content of copper (6877 mg/kg) and nickel (2580 mg/kg). The tested preparations differ in their remediation capacity. Soil phytotesting demonstrates that iron nanoparticles significantly outperform the detoxifying effect of microparticles (iron powder). However, analysis of water extracts does not show any advantage of nanoparticles in reducing the soil toxicity. The dependence of the assessed detoxifying capacity of zero-valent iron nanoparticles on soil properties and the plant species used in phytotesting is discussed. The phytoeffect of nanoparticles in standard
S. alba
tests is 1.5-fold higher as compared with iron microparticles (root length of 117 ± 4.3 and 80 ± 7.6 mm, respectively). However, the chronic phytotoxicity assessment of the same soils using perennial ryegrass
Lolium perenne
L. fails to find any differences between the effects of micro- and nanoparticles of zero-valent iron.
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