Vacuum polarization in muonic and antiprotonic atoms: the fine structure at medium Z

Effects of vacuum polarization modify the energy levels in atoms with an orbiting particle heavier than an electron. The dominant effect is due to the Uehling potential. In this paper we consider the relativistic corrections to the energy levels caused by the Uehling potential and in particular the fine structure in muonic and antiprotonic atoms. We derive general expressions and consider in detail specific regions of parameters which allow simple asymptotic expansion. We take into account the recoil effects and anomalous magnetic moment in the case of an antiproton as the orbiting particle

The Lamb shift contribution of very light millicharged particles

The leading order vacuum polarization contribution of very light millicharged fermions and scalar (spin-0) particles with charge \epsilon e and mass \mu to the Lamb shift of the hydrogen atom is shown to imply universal, i.e. \mu-independent, upper bounds on \epsilon: \epsilon \lsim 10^{-4} for \mu \lsim 1 keV in the case of fermions, and for scalars this bound is increased by a factor of 2. This is in contrast to expectations based on the commonly used approximation to the Uehling potential relevant only for conventionally large fermion (and scalar) masses.Comment: 10 pages including 3 figures, version to appear in Physical Review D (Rapid Communications

Composition of powders produced by electrospark dispersion of metal granules in water

The results of experimental studies of metal powders composition produced by electrospark dispersion according to the scheme "metal electrodes - metal granule loading - distilled water" are given in the paper. With a help of X-ray diffraction analysis and other methods, it was found that chemical and phase composition of dispersion products is determined by affinity of metal to oxygen

Relativistic recoil corrections to the electron-vacuum-polarization contribution in light muonic atoms

The relativistic recoil contributions to the Uehling corrections are revisited. We consider a controversy in recent calculations based on different approaches including Breit-type and Grotch-type calculations. We have found that calculations of those authors were in fact done in different gauges and in some of those gauges contributions the retardation and two-photon-exchange effects were missed. We have evaluated such effects and obtained a consistent result from those approaches. We present a correct expression for the Grotch-type approach which produces a correct gauge-invariant result. We also consider a finite-nuclear-size correction for the Uehling term. The results are presented for muonic hydrogen and deuterium atoms and for muonic helium-3 and helium-4 ions.Comment: Submitted to Phys. Rev. A; in v.2 results for muonic helium are correcte

Breit Hamiltonian and QED Effects for Spinless Particles

We describe a simplified derivation for the relativistic corrections of order $\alpha^4$ for a bound system consisting of two spinless particles. We devote special attention to pionium, the bound system of two oppositely charged pions. The leading quantum electrodynamic (QED) correction to the energy levels is of the order of $\alpha^3$ and due to electronic vacuum polarization. We analyze further corrections due to the self-energy of the pions, and due to recoil effects, and we give a complete result for the scalar-QED leading logarithmic corrections which are due to virtual loops involving only the scalar constituent particles (the pions); these corrections are of order $\alpha^5 \ln \alpha$ for S states.Comment: 12 pages, LaTeX; references added (J. Phys. B, in press

Microscopic Calculation of Total Ordinary Muon Capture Rates for Medium - Weight and Heavy Nuclei

Total Ordinary Muon Capture (OMC) rates are calculated on the basis of the Quasiparticle Random Phase Approximation for several spherical nuclei from 90^Zr to 208^Pb. It is shown that total OMC rates calculated with the free value of the axial-vector coupling constant g_A agree well with the experimental data for medium-size nuclei and exceed considerably the experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates to the nuclear residual interactions is discussed.Comment: 27 pages and 3 figure

Kisspeptin-mediated regulation of testicular activity of rats under the effect of gold nanoparticles

З’ясовано особливості впливу наночастинок золота на функціональну активність сім’яників щурів різного віку. За інтраперитонеального уведення наночастинок золота в дозі 0,1 мг/100 г маси тіла гістологічна структура сім’яника залишається в межах норми. Встановлено пригнічувальний вплив нанозолота на ендокринну та сперматогенну активність сім’яників дорослих тварин, хоча змін морфометричних параметрів у молодих тварин не виявлено. За дії нанорозмірного золота активація кіспептинергічної системи гіпоталамуса шляхом інтрацеребровентрикулярного уведення кіспептину в бічний шлуночок мозку не викликає підвищення функціональної активності сім’яників тварин обох вікових груп. Блокування кіспептин-опосередкованої регуляції посилює пригнічувальний вплив нанозолота, при цьому в сім’яниках з’являються морфологічні ознаки пригнічення сперматогенезу. Вплив нанорозмірного золота на регуляцію активності сім’яників не залежить від віку тварини. Наші дані свідчать, що наночастинки золота порушують систему регуляторних взаємодій репродуктивної системи самців щурів, що необхідно брати до уваги у подальшому практичному застосуванні цих наноматеріалів. З’ясовано особливості впливу наночастинок золота на функціональну активність сім’яників щурів різного віку. За інтраперитонеального уведення наночастинок золота в дозі 0,1 мг/100 г маси тіла гістологічна структура сім’яника залишається в межах норми. Встановлено пригнічувальний вплив нанозолота на ендокринну та сперматогенну активність сім’яників дорослих тварин, хоча змін морфометричних параметрів у молодих тварин не виявлено. За дії нанорозмірного золота активація кіспептинергічної системи гіпоталамуса шляхом інтрацеребровентрикулярного уведення кіспептину в бічний шлуночок мозку не викликає підвищення функціональної активності сім’яників тварин обох вікових груп. Блокування кіспептин-опосередкованої регуляції посилює пригнічувальний вплив нанозолота, при цьому в сім’яниках з’являються морфологічні ознаки пригнічення сперматогенезу. Вплив нанорозмірного золота на регуляцію активності сім’яників не залежить від віку тварини. Наші дані свідчать, що наночастинки золота порушують систему регуляторних взаємодій репродуктивної системи самців щурів, що необхідно брати до уваги у подальшому практичному застосуванні цих наноматеріалів. There are a variety of biomedical applications of nanoparticles. They can be used as drug carriers, anti-tumor agents, biosensors and modulators of immune response. But full-scale real clinical application of nanomaterials requires a great deal of information on their safety and biotoxicity. Even traditionally harmless materials, like gold, can obtain toxic features when scaled to the nanosize. In vitro studies showed that nanoparticles can be geno- and cytotoxic, but their effects on the body as a whole remain largely a mystery. To shed some light on this, our study focused on the reproductive toxicity of nanomaterials. We synthesized 10–15 nm gold nanoparticles through the reduction of sodium tetrachloroaurate (III) in an alkaline medium with the addition of sodium polyphosphate as a stabilizing agent. Next, these particles were administered intraperitoneally to young and old rats for 10 days. To test functional capabilities of the testes, we injected kisspeptin-10 or its antagonist peptide-234 intracerebroventricularly. These substances are known to stimulate or inhibit the central component of the hypothalamic-pituitary-gonadal axis respectively. After the routine histological procedures, we measured the diameter of seminiferous tubules and the nuclear cross-sectional area of Sertoli cells as markers of testicular spermatogenic activity and a cross-sectional area of the Leydig cells’ nuclei as a marker of testicular steroidogenesis. We found that injections of nanogold caused no significant changes in the young animals. At the same time, morphometric parameters of adult animals were significantly lower compared to control, although we observed no pathological changes in the tissue. Combined administration of gold nanoparticles and kisspeptin showed that the stimulatory effect of the latter was not observed at all. This is a specific feature of toxicants called “endocrine disruptors”. Moreover, we found morphological signs of testicular degeneration, which are characteristic of the low-testosterone state. Simultaneous injections of gold and peptide-234 resulted in the highest degree of testicular functional downregulation, regardless of age. Taken as a whole, our data indicates that gold nanoparticles disrupt the regulatory network of the hypothalamic-pituitary-gonadal axis, possibly due to direct action on the interstitial cells and spermatogenic epithelium.

Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell during initial stage of shell expansion

Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell, created under laser heating of nanoparticle in water, were theoretically investigated. Vapor shell expansion leads to decreasing up to one to two orders of magnitude in comparison with initial values of scattering and extinction of the radiation with wavelengths 532 and 633 nm by system while shell radius is increased up to value of about two radii of nanoparticle. Subsequent increasing of shell radius more than two radii of nanoparticle leads to rise of scattering and extinction properties of system over initial values. The significant decrease of radiation scattering and extinction by system of nanoparticle-vapor shell can be used for experimental detection of the energy threshold of vapor shell formation and investigation of the first stages of its expansion

Dislocation Kinks in Copper: Widths, Barriers, Effective Masses, and Quantum Tunneling

We calculate the widths, migration barriers, effective masses, and quantum tunneling rates of kinks and jogs in extended screw dislocations in copper, using an effective medium theory interatomic potential. The energy barriers and effective masses for moving a unit jog one lattice constant are close to typical atomic energies and masses: tunneling will be rare. The energy barriers and effective masses for the motion of kinks are unexpectedly small due to the spreading of the kinks over a large number of atoms. The effective masses of the kinks are so small that quantum fluctuations will be important. We discuss implications for quantum creep, kink--based tunneling centers, and Kondo resonances