251 research outputs found
Maximal nowhere dense -sets in basically disconnected spaces and -spaces
summary:In [5] the following question was put: are there any maximal n.d. sets in ? Already in [9] the negative answer (under {\bf MA}) to this question was obtained. Moreover, in [9] it was shown that no -set can be maximal n.d. In the present paper the notion of a maximal n.d. -set is introduced and it is proved that under {\bf CH} there is no such a set in . The main results are Theorem 1.10 and especially Theorem 2.7(ii) (with Example in Section 3) in which the problem of the existence of maximal n.d. -sets in basically disconnected compact spaces with rich families of n.d. -sets is actually solved
Radiation Pressure Dominate Regime of Relativistic Ion Acceleration
The electromagnetic radiation pressure becomes dominant in the interaction of
the ultra-intense electromagnetic wave with a solid material, thus the wave
energy can be transformed efficiently into the energy of ions representing the
material and the high density ultra-short relativistic ion beam is generated.
This regime can be seen even with present-day technology, when an exawatt laser
will be built. As an application, we suggest the laser-driven heavy ion
collider.Comment: 10 pages, 4 figure
Autoresonance in a Dissipative System
We study the autoresonant solution of Duffing's equation in the presence of
dissipation. This solution is proved to be an attracting set. We evaluate the
maximal amplitude of the autoresonant solution and the time of transition from
autoresonant growth of the amplitude to the mode of fast oscillations.
Analytical results are illustrated by numerical simulations.Comment: 22 pages, 3 figure
Tunable high-energy ion source via oblique laser pulse incidence on a double-layer target
The laser-driven acceleration of high quality proton beams from a
double-layer target, comprised of a high-Z ion layer and a thin disk of
hydrogen, is investigated with three-dimensional particle-in-cell simulations
in the case of oblique incidence of a laser pulse. It is shown that the proton
beam energy reaches its maximum at a certain incidence angle of the laser
pulse, where it can be much greater than the energy at normal incidence. The
proton beam propagates at some angle with respect to the target surface normal,
as determined by the proton energy and the incidence angle
Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications
Resonant frequencies of the two-dimensional plasma in FETs increase with the
reduction of the channel dimensions and can reach the THz range for sub-micron
gate lengths. Nonlinear properties of the electron plasma in the transistor
channel can be used for the detection and mixing of THz frequencies. At
cryogenic temperatures resonant and gate voltage tunable detection related to
plasma waves resonances, is observed. At room temperature, when plasma
oscillations are overdamped, the FET can operate as an efficient broadband THz
detector. We present the main theoretical and experimental results on THz
detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape
Perturbative analysis of wave interactions in nonlinear systems
This work proposes a new way for handling obstacles to asymptotic
integrability in perturbed nonlinear PDEs within the method of Normal Forms -
NF - for the case of multi-wave solutions. Instead of including the whole
obstacle in the NF, only its resonant part is included, and the remainder is
assigned to the homological equation. This leaves the NF intergable and its
solutons retain the character of the solutions of the unperturbed equation. We
exploit the freedom in the expansion to construct canonical obstacles which are
confined to te interaction region of the waves. Fo soliton solutions, e.g., in
the KdV equation, the interaction region is a finite domain around the origin;
the canonical obstacles then do not generate secular terms in the homological
equation. When the interaction region is infifnite, or semi-infinite, e.g., in
wave-front solutions of the Burgers equation, the obstacles may contain
resonant terms. The obstacles generate waves of a new type, which cannot be
written as functionals of the solutions of the NF. When an obstacle contributes
a resonant term to the NF, this leads to a non-standard update of th wave
velocity.Comment: 13 pages, including 6 figure
Proton Driven Plasma Wakefield Acceleration
Plasma wakefield acceleration, either laser driven or electron-bunch driven,
has been demonstrated to hold great potential. However, it is not obvious how
to scale these approaches to bring particles up to the TeV regime. In this
paper, we discuss the possibility of proton-bunch driven plasma wakefield
acceleration, and show that high energy electron beams could potentially be
produced in a single accelerating stage.Comment: 13 pages, 4 figure
Tailored biological retention and efficient clearance of pegylated ultra-small MnO nanoparticles as positive MRI contrast agents for molecular imaging
A majority of MRI procedures requiring intravascular injections of contrast agents are performed with paramagnetic chelates. Such products induce vascular signal enhancement and they are rapidly excreted by the kidneys. Unfortunately, each chelate is made of only one paramagnetic ion, which, taken individually, has a limited impact on the MRI signal. In fact, the detection of molecular events in the nanomolar range using T-1-weighted MRI sequences requires the design of ultra-small particles containing hundreds of paramagnetic ions per contrast agent unit. Ultra-small nanoparticles of manganese oxide (MnO, 6-8 nm diameter) have been developed and proposed as an efficient and at least 1000 x more sensitive “positive” MRI contrast agent. However no evidence has been found until now that an adequate surface treatment of these particles could maintain their strong blood signal enhancement, while allowing their rapid and efficient excretion by the kidneys or by the hepatobiliairy pathway. Indeed, the sequestration of MnO particles by the reticuloendothelial system followed by strong uptake in the liver and in the spleen could potentially lead to Mn2+-induced toxicity effects. For ultra-small MnO particles to be applied in the clinics, it is necessary to develop coatings that also enable their efficient excretion within hours. This study demonstrates for the first time the possibility to use MnO particles as T-1 vascular contrast agents, while enabling the excretion of > 70% of all the Mn injected doses after 48 h. For this, small, biocompatible and highly hydrophilic pegylated bis-phosphonate dendrons (PDns) were grafted on MnO particles to confer colloidal stability, relaxometric performance, and fast excretion capacity. The chemical and colloidal stability of MnO@PDn particles were confirmed by XPS, FTIR and DLS. The relaxometric performance of MnO@PDns as “positive” MRI contrast agents was assessed (r(1) = 4.4 mM(-1) s(-1), r(2)/r(1) = 8.6; 1.41 T and 37 degrees C). Mice were injected with 1.21 mu g Mn per kg (22 mu mol Mn per kg), and scanned in MRI up to 48 h. The concentration of Mn in key organs was precisely measured by neutron activation analysis and confirmed, with MRI, the possibility to avoid RES nanoparticle sequestration through the use of phosphonate dendrons. Due to the fast kidney and hepatobiliairy clearance of MnO particles conferred by PDns, MnO nanoparticles can now be considered for promising applications in T1-weighted MRI applications requiring less toxic although highly sensitive “positive” molecular contrast agents
Glass Film Formation on GOES Surface during High-Temperature Annealing: The Mechanism with Amorphous Phase Formation
Ceramic insulation coating (glass film) is an important constituent of grain-oriented electrical steel (GOES) designed for use in transformers. Within the scope of this study, the glass film was obtained by means of interaction between the surface of GOES containing 0.5 wt. % Cu and a heat-resistant MgO coating during annealing up to 1100 °C in the 75%H2 + 25%N2 atmosphere. The structure of glass film was analyzed using X-ray diffraction, glow-discharge optical emission spectroscopy, scanning probe microscopy, scanning electron microscopy, differential scanning calorimetry and thermodynamic calculations. After annealing, the glass film contained the following phases: crystalline (MgFe)2SiO4 and amorphous Fe-based solid solutions. The multi-stage mechanism of the glass film formation on GOES surface during high-temperature annealing was determined. © 2022 by the authors.Ministry of Education and Science of the Russian Federation, MinobrnaukaThis research was funded by the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program)
Unlimited Energy Gain in the Laser-Driven Radiation Pressure Dominant Acceleration of Ions
The energy of the ions accelerated by an intense electromagnetic wave in the
radiation pressure dominated regime can be greatly enhanced due to a transverse
expansion of a thin target. The expansion decreases the number of accelerated
ions in the irradiated region increasing the energy and the longitudinal
velocity of remaining ions. In the relativistic limit, the ions become
phase-locked with respect to the electromagnetic wave resulting in the
unlimited ion energy gain. This effect and the use of optimal laser pulse shape
provide a new approach for great enhancing the energy of laser accelerated
ions.Comment: 30 pages, 9 figures, misprints correcte
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