Transient Cherenkov radiation from an inhomogeneous string excited by an ultrashort laser pulse at superluminal velocity

An optical response of one-dimensional string made of dipoles with a periodically varying density excited by a spot of light moving along the string at the superluminal (sub-luminal) velocity is theoretically studied. The Cherenkov radiation in such system is rather unusual, possessing both transient and resonant character. We show that under certain conditions, in addition to the resonant Cherenkov peak another Doppler-like frequency appears in the radiation spectrum. Both linear (small-signal) and nonlinear regimes as well as different string topologies are considered.Comment: accepted to Phys. Rev.

Electronic Structure of Nitrogen- and Phosphorus-Doped Graphenes Grown by Chemical Vapor Deposition Method

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data. View Full-Tex

Morphology of ceramic particles produced by plasma-chemical synthesis

Thermal and diffusion processes in the droplet weakly concentrated metal salt solution during its heating in the plasma chemical reactor, in order to synthesize metal oxide powders are considered. Numerical study is based on previously proposed physical-mathematical model. The results of numerical calculations are analyzed to assess the possible influence of the operation parameters of the reactor and the characteristics of the initial solution (precursor) on the morphology of the particles formed

Investigation of working processes in a flowing channel of ramjet engine

The technique and results of experimental-theoretical study of gas-dynamics, heat transfer and the structure of gas-flow in the flowing channel of a ramjet engine in Mach number range M = (5-7) are presented. The temperature distribution along the flowing channel of a ramjet engine was experimentally obtained. The temperature along the wall of the flowing channel of the axisymmetric model was measured using the developed thermoprobe. Distributions of Mach number and temperature along the symmetry axis of the flowing channel of the model are obtained numerically. Comparison of the numerical and experimentally obtained values of the Mach number showed their qualitative agreement

Current Approaches to Assessing the Safety and Efficacy of Lamotrigine in Children and Adolescents with Epileptic Syndromes Associated with Focal Seizures

Scientific relevance. Epileptic syndromes associated with focal seizures often develop in children and adolescents and may be accompanied by cognitive impairment, mental disorders, and endocrine disorders, which require additional medication apart from anti-epileptic medicinal products. Currently, the selection of safe and effective therapies for epileptic syndromes, especially in paediatric populations, is a pressing challenge for epileptology.Aim. This study aimed at a comprehensive assessment of the safety and efficacy of lamotrigine in therapeutic doses for children and adolescents with epileptic syndromes associated with focal seizures.Materials and methods. A total of 53 patients aged 3 to 18 years with various epileptic syndromes associated with focal seizures were under observation in 2020–2023. During this period, 37 patients (69.8%) received monotherapy with lamotrigine, and 16 patients (30.2%) received combination therapy including lamotrigine and two or more other medicinal products. When evaluating the safety and efficacy of pharmacotherapy in adolescent patients, the authors selectively used the Software for Post-marketing Studies of Anti-epileptic Medicinal Products developed at the Scientific Centre for Expert Evaluation of Medicinal Products.Results. With lamotrigine, the highest rate of complete clinical remission was observed in patients with focal epilepsy with onset in childhood and adolescence (90.9% of cases). For structural focal epilepsy, 16.7% of patients achieved complete freedom from seizures, and 50% demonstrated a pronounced response to treatment. However, patients with epilepsy due to local structural changes in the neocortex (33.3% of cases) had a prognosis of severe epilepsy. For epileptic encephalopathies with onset in childhood, 66.7% of patients achieved a ≥50% reduction in the frequency of seizures. Seizure reduction improved the quality of life of patients and their parents, especially of those with a long history of unsuccessful treatment attempts. There were no adverse reactions associated with lamotrigine except those listed in the summary of product characteristics. The Software for Post-marketing Studies of Anti-epileptic Medicinal Products provided a means for scoring and plotting the changes in the condition of adolescents without severe cognitive and memory impairment undergoing lamotrigine treatment.Conclusions. According to the study results, lamotrigine is highly effective and has a favourable safety profile in patients with early-onset epileptic syndromes associated with focal seizures. Moreover, lamotrigine is applicable to the treatment of attention, memory, expressive speech disorders, and aggressive behaviour. Therefore, lamotrigine may be recommended for treating children and adolescents with comorbid epileptic syndromes and cognitive and emotional disorders. Specialised software improves the quality of real-world evidence regarding the safety and efficacy of anti-epileptic medication

Mathematical modelling of the liquid atomization process by cocurrent gas flow

This paper focuses on the physical-mathematical model of liquid atomization in the spray pattern of an ejection nozzle. A flow field of a gas phase behind the nozzle section is computed using the Ansys Fluent package. Dynamics of molten metal droplets in the gas phase within a trajectory approach is calculated. Using the presented model, numerical calculation results are given

Selective substitution in orbital domains of a low doped manganite : an investigation from Griffiths phenomenon and modification of glassy features

An effort is made to study the contrast in magnetic behavior resulting from minimal disorder introduced by substitution of 2.5% Ga or Al in Mn-site of La${_{0.9}}$Sr$_{0.1}$MnO${_3}$. It is considered that Ga or Al selectively creates disorder within the orbital domains or on its walls, causing enhancement of Griffiths phase (GP) singularity for the former and disappearance of it in the later case. It is shown that Ga replaces Mn$^{3+}$ which is considered to be concentrated within the domains, whereas Al replaces Mn$^{4+}$ which is segregated on the hole-rich walls, without causing any significant effect on structure or ferromagnetic transition temperatures. Thus, it is presumed that the effect of disorder created by Ga extend across the bulk of the domain having correlation over similar length-scale resulting in enhancement of GP phenomenon. On the contrary, effect of disorder created by Al remains restricted to the walls resulting in the modification of the dynamics arising from the domain walls and suppresses the GP. Moreover contrasting features are observed in the low temperature region of the compounds; a re-entrant spin glass like behavior is observed in the Ga doped sample, while the observed characteristics for the Al doped sample is ascribed only to modified domain wall dynamics with the absence of any glassy phase. Distinctive features in third order susceptibility measurements reveals that the magnetic ground state of the entire series comprises of orbital domain states. These observations bring out the role of the nature of disorder on GP phenomenon and also reconfirms the character of self-organization in low-doped manganites

Pairing of charged particles in a quantum plasmoid

We study a quantum spherically symmetric object which is based on radial plasma oscillations. Such a plasmoid is supposed to exist in a dense plasma containing electrons, ions, and neutral particles. The method of creation and annihilation operators is applied to quantize the motion of charged particles in a self-consistent potential. We also study the effective interaction between oscillating particles owing to the exchange of a virtual acoustic wave, which is excited in the neutral component of plasma. It is shown that this interaction can be attractive and result in the formation of ion pairs. We discuss possible applications of this phenomenon in astrophysical and terrestrial plasmas.Comment: 17 pages, no figures, two columns, LaTeX2e; paper was significantly revised; title was changed; 16 new references were included; the discussion on ion-acoustic waves was added to Sec. 2; Secs. 3 and 4 were shortened; a more detailed discussion was added to Sec. 7; accepted for publication to J.Phys.

Tensor analyzing power Ayy in deuteron inclusive breakup at large Pt and spin structure of deuteron at short internucleonic distances

The Ayy data for deuteron inclusive breakup off hydrogen and carbon at a deuteron momentum of 9.0 GeV/c and large Pt of emitted protons are presented. The large values of Ayy independent of the target mass reflect the sensitivity of the data to the deuteron spin structure. The data obtained at fixed $x$ and plotted versus Pt clearly demonstrate the dependence of the deuteron spin structure at short internucleonic distances on two variables. The data are compared with the calculations using Paris, CD-Bonn and Karmanov's deuteron wave functions.Comment: 4 pages, 2 figures, talk given at the SPIN2004 Conf., 10-16 Oct. 2004, Triest, Ital