Stationary Nuclei Research Articles

A novel “gel–sol” strategy to synthesize TiO2 nanorod combining reduced graphene oxide composites

In this study, a novel so-called “gel–sol” process is firstly reported for synthesis of TiO2 nanorod (TN) combining reduced graphene oxide (RGO) composites. By utilizing the triethanolamine (TEOA) as shape controller and under specific conditions (such as pH=12), the hybrid composites can be readily obtained. The higher pH value benefits the deprotonation of TEOA for adsorption to the stationary nuclei. Therefore, the synthesized hybrid composites have the morphology of crystalline anatase TiO2 nanorods anchored into the surface of reduced graphene oxide. The hybrid composites fabricated by the novel process have distinct advantages over the traditional methods for obtaining TiO2 and graphene-based composites in terms of the well-confined TiO2 morphology and the formation of Ti–C bonds between TN and RGO simultaneously.

Number of elastic scatterings on free stationary nuclei to slow down a neutron

We report the formulation of the number of elastic scatterings required to slow down a neutron. By establishing its analytical expression, we show that this number displays a discontinuity and an oscillatory transient that progressively dampens when the neutron energy decreases. This result does not apply to neutrons with energies lower than a few eV, as we restrict our study to scatterings on free stationary nuclei.

Polymer-assisted deposition of homogeneous metal oxide films to produce nuclear targets

Targets are essential in experimental nuclear sciences as a source of stationary nuclei for nuclear reactions with ion beams. Typically, targets should be chemically pure, uniform, homogeneous and crack-free over the irradiation area, while also being structurally rigid. The polymer-assisted deposition (PAD) method uses a water-soluble multidentate polymer that chelates metal precursors in solution. This polymer-metal solution is then spin coated and annealed to yield a crack-free, homogeneous metal oxide film. In this protocol, nuclear targets are created using PAD on silicon nitride (Si(3)N(4)) windows with silicon frames. Silicon wafers ([100], single-side polished) coated with 1 microm of silicon nitride on both sides are patterned and etched to create 1-microm silicon nitride windows. The PAD solution is then spun onto the silicon nitride window and annealed to create a thin, uniform metal oxide film of variable thickness on top of the silicon nitride backing. The production of a target window and the deposition of a thin film ranging from 50 to 150 nm takes approximately 13.5 h. Subsequent reapplications to grow thicker films require an additional 5 h per application.

Subharmonic Resonance Behavior for the Classical Hydrogen Atomic System

Previously unexplored resonance conditions are shown to exist for the classical hydrogen atomic system, where the electron is treated as a classical charged point particle following the nonrelativistic Lorentz-Dirac equation of motion about a stationary nucleus of opposite charge. For circularly polarized (CP) light directed normal to the orbit, very pronounced subharmonic resonance behavior is shown to occur with a variety of interesting properties. In particular, only if the amplitude of the CP light exceeds a critical value, will the resonance continue without radius and energy decay. A perturbation analysis is carried out to illustrate the main features of the behavior. The present phenomena adds to a growing list of other nonlinear dynamical behaviors of this simple system, that may well be important for more deeply understanding classical and quantum connections.

A momentum-conserving Franck-Condon approximation: Theory and application to the photodissociation of Li2+ in an intense laser field

A new, computationally efficient approximation to calculating matrix elements between vibrational-electronic states that does not assume stationary nuclei is introduced. The approach emphasizes the importance of the conservation of nuclear momenta. The calculated quantities can be used wherever equivalent quantities from standard Franck-Condon treatments can be used. The new method is illustrated by a time-dependent perturbation theory description of the photodissociation of the Li(2) (+) molecular cation in an intense laser field (I=0.9x10(12) W/cm(2)), which was previously identified in a detailed study of the electronic structure [Khait et al., J. Chem. Phys. 122, 094111 (2005)] as likely to have unusual sensitivity to the initial vibrational state in dynamics. The current study confirms this speculation and shows this to be a specific instance of a situation in which nuclear dynamics during an electronic optical transition cannot be ignored.

Secondary Particle Energy Deposition for Proton and Carbon Therapy Beams

One of the radiobiological difficulties associated with proton and carbon ion therapy is the production of secondary particles. When heavy charged particles collide with stationary target nuclei, part of the nuclear volume of the target can be sheared away by the collision. This fragmentation process (known as spallation) results in the emission of a large number of nucleons. The rate of fragmentation depends on the composition of the medium and the energy and mass of the accelerated particles. The purpose of this work was to evaluate the energy deposition contributions from primary particles versus the contribution of secondary particles.

Nuclear phenomena during conjugation of Heliophrya erhardi (Ciliata, Suctoria). II. The orientation of postmeiotic and metagamic division spindles is organized by the cytoskeleton

Summary Whereas the spindles of the meiotic divisions appear in a random orientation within the co-conjugants of Heliophrya erhardi, the spindles of the postmeiotic and metagamic nuclei show a distinct fixed position within the conjugational bridge and in the cytoplasm of each partner’s cell body. In postmeiotic divisions, the spindle orientation results in a different functional determination of the division products. For their later fate, mostly a concentration gradient of “cytoplasmic factors” was postulated [29]. But above all, the question arises, what is the mechanistic basis for the spindle orientation? We followed the sequential steps of conjugation by time lapse microcinematography and by EM-observation. The result of the maturation divisions are 12 to 24 haploid nuclei [11] from which only one nucleus reaching the conjugational bridge survives and starts the postmeiotic division. The position of this gonal nucleus is fixed on the left marginal side of the bridge by a dense microfilament network surrounding the nucleus in a cage-like manner and anchoring it to the epiplasmic septum separating the co-conjugants. During the following division, the spindle extends parallel to the septum fixed by cytoskeletal elements during anaphasic spindle elongation. Additionally, at metaphase, a basal body appearing at the spindle pole proximal to the pellicle nucleates microtubules (MTs) which penetrate the microfilamentous cage and contact also the nuclear envelope. The fixation of the spindle axis parallel to the separating septum by cytoskeletal elements guarantees the positioning of one pronucleus as the future stationary nucleus on the left side, and the other — the presumptive migratory nucleus — on the right side of the conjugational bridge. After exchange of the migratory nuclei and subsequent fusion with formation of the diploid synkaryon, one metagamic division follows immediately in each partner cell. From meta- to telophase the spindles exhibit in most cases a strict central-peripheral orientation, at which the anterior daughter nucleus (oriented to the cell’s center) becomes the macronucleus anlage, while the posterior nucleus condenses to the micronucleus. Interestingly, this spindle orientation is held in position by aster-like organized microtubules radiating out to a microfilamentous cap situated at the anterior spindle pole. As an organizing center for this cytoskeletal structure again a basal body is responsible, which is localized between nuclear envelope and cap region from meta- to telophase. It is evident, that in both divisions, the orientation of the spindle axis and consequently the fate of the division products depends completely on the existence of a cytoskeletal organizing structure, which is comparable to the asters of mitotic spindles in some higher eukaryotes.

Interphase chromosome domain re-organization following irradiation

Purpose: To investigate chromosome domain movements during interphase in stationary cell nuclei. Materials and methods: Contact-inhibited primary human fibroblasts were irradiated with 4.0Gy X-rays, BrdU was added, and airdried cell preparations made at intervals up to 48h. Chromosome 4 domain signals (1, 2 and >2) in BrdU negative nuclei (almost exclusively G0/G1) were counted using FISH. A similar experiment was performed using unstimulated human lymphocytes. Results: A very significant rise in nuclei with >2 signals was found within 1h after radiation. The frequencies observed were in very good agreement with those expected for simple and complex interchanges involving chromosome 4, scored at metaphase in these materials. Conclusions: The observations constitute evidence for significant domain movement and re-organization within a short time of radiation exposure in G0/G1 interphase nuclei, presumably induced by the formation of inter-domain exchanges. Such re-organization must be a very complicated and delicate topological problem for relaxed chromatin, and must have an important bearing on the interpretation of mechanistic premature chromosome condensation experiments performed whilst it is in operation.

Wide frequency range 31P relaxation in the ion conducting glass LiPO 3

Spin–lattice relaxation studies on the stationary 31P nucleus have been performed in order to investigate to which extent the dynamics of the mobile lithium ions are reflected in the behavior of the glassy network. The temperature dependence of the 31P relaxation, which is governed by the heteronuclear dipole–dipole interaction between lithium and phosphorus, can be described in terms of a Gaussian distribution of activation energies and that over a wide frequency range from about 34 kHz to 81 MHz. A relaxation rate maximum, which provides useful information about correlation times and activation energies of the lithium-ion diffusion process, could only be observed in the rotating frame relaxation measurements.

The ground state of ethylene

The ground state geometry of ethylene is reviewed and calculated using a basis set near the Hartree-Fock limit and post-Hartree-Fock methods. The best estimate of the equilibrium geometry is R CC = 1.3307 A ̊ , R CH = 1.0809 A ̊ , < HCC = 121.44 ° by Martin and Taylor [Chem. Phys. Lett., 248 (1996) 336]. The estimated non-relativistic, stationary nucleus, equilibrium geometry total energy is −78.5877 hartrees.

High sensitivity nuclear quadrupole resonance approach for detection of modulation wave motion in incommensurate systems.

In contrast to conventional NMR techniques that use magnetic field gradients(MFG's) to detect the diffusion of moving atoms, we have developed a highlysensitive approach for detecting electric field gradient (EFG) fluctuationsseen by stationary atoms. These EFG fluctuations were observed in the quadrupoleperturbed NMR behavior of a stationary nucleus ${(}^{93}$Nb)in the incommensurate insulator barium sodium niobate and are attributed tomotion of the modulation wave. We observed effective diffusion constants oforder ${10}^{\ensuremath{-}13}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{2}/\mathrm{s}$, which are 4 orders of magnitude smaller than those currently detectable with MFG NMR.

The AAPM/RSNA physics tutorial for residents. An introduction to MR angiography.

This article provides an overview of the basic principles of magnetic resonance (MR) angiography. The parameters in MR imaging manipulated to generate high contrast between flowing nuclei and stationary tissue are discussed. Two primary strategies are used: time-of-flight (TOF) MR angiography, which creates differences in magnetization magnitude between flowing and stationary nuclei, and phase-contrast MR angiography, which induces changes in the spatial orientation, or phase, of flowing nuclei relative to stationary nuclei. The end result of an MR angiographic study is typically a three-dimensional data set composed of either sequential two-dimensional sections or true three-dimensional data. Two-dimensional TOF methods are sensitive to slow flow and are valuable for differentiating between slow flow and occlusion. Three-dimensional TOF methods have better resolution and are more useful in imaging tortuous vessels. Phase-contrast MR angiography can be effectively used to avoid problems of magnetization saturation that occur in three-dimensional TOF studies and to eliminate signal from high-intensity stationary material such as blood products, which may appear bright and mimic flow signal in TOF studies. Careful use of postprocessing tools aids in the assessment of vascular abnormalities once the MR angiographic data have been acquired.

A New Understanding of Far-Field Potentials and their use in Clinical Diagnosis

Far-field potentials are "stationary" potentials detected by referential montages that do not substantially change in amplitude or latency over relatively large areas of recording locations. Much elucidative work regarding the origin and source of biophysiologic far-field potentials has occurred over the last decade. Emphasis has shifted from stationary synaptic nuclei generators to origins occurring from the interaction of an advancing action potential volley’s electrophysical interaction with the surrounding volume conductor. This interaction can be conceptualized by a relatively simple double dipole model of a propagating action potential with excellent agreement with experimental findings. A review of far-field potential research to date has clarified possible mechanisms that produce such potential, but significant advances in their clinical use have yet to be demonstrated.

Intravascular susceptibility contrast mechanisms in tissues.

The factors affecting the rate of loss of transverse magnetization in gradient echo and spin-echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations. The results are particularly relevant for describing the signal losses that occur in tissues containing capillaries of altered intrinsic susceptibility from the administration of exogenous contrast agents or arising from changes in blood oxygenation. The precise magnitudes and relationship of gradient echo and spin-echo decay rates depend on geometrical factors such as the sizes and spacings of the inhomogeneities, the rate of water diffusion, field strength, and echo times. The conventional separation of contributions to transverse decay rates arising from so-called static field effects and diffusion is shown to be inappropriate for many situations of practical interest because diffusion introduces a motional averaging of the static field even in gradient echo sequences. The result of diffusion in some regimes is to reduce the decay rate from field inhomogeneities in gradient echo sequences, so that T2* is longer in media such as tissue where water diffuses reasonably rapidly, than would be the case for stationary nuclei. The effects of different types of contrast agent and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are considered.

The theory of the nucleation of monodisperse particles in open systems and its application to agbr systems

The theory of the nucleation process has been developed for monodisperse sparingly soluble colloidal particles in an open system, where the monomer source (a combination of the reactants or a single reactive component to be reacted with a counterpart in the system) is introduced from outside at a constant molal feed rate ( Q), and the rates of growth and dissolution of the particles are both limited by the diffusion of the monomer complexes. The theory is based on a nucleation model where stable nuclei as origins of the product particles are produced through a kind of Ostwald ripening from stationary unstable nuclei that are in a quasi-steady state of balance between the generation of their embryos by instantaneous reaction of the introduced reactants and either dissolution or growth. It leads to the final particle number, n + ∞, the mean radius of the stable nuclei at the end of the nucleation, r + n , and the nucleation time for the production of the stable nuclei, t n; i.e., n + ∞ = 1.567QRT 8πDσV m C ∞ , r + n = 1.638 r p, and t n = 5.097RTv p 8πDσV m 2C ∞ , where R is the gas constant, T is the absolute temperature, D is the diffusion coefficient of the monomers, a is the specific surface energy of the solid, V m is the molar volume of the solid, C ∞. is the solubility of the solid, and r p and v p are the maximum radius and the maximum volume, respectively, of the embryos within their size distribution range. The theoretical conclusions have been confirmed by experiment for the formation of monodisperse AgBr particles, and the mean radius as well as the maximum radius of their embryos was evaluated.

Analysis of some metabolic conditions promoting selective sensitivity of tumor cells to peroxidative stress

Some metabolic parameters enhancing the sensitivity of tumor cells and their lipoprotein refractive granules (RG) to peroxidative stress were investigated during the growth cycle of ascite tumors in vivo. The majority of tumor cells only in the stationary growth phase had the increased sensitivity to peroxidative stress, tested by fluorescence intensivity of peroxidation products. The increase of this intensity correlates well with the decrease of tumor proliferation, the functional activity of mitochondria, the cellular level of ATP and extracellular pH. These metabolic conditions are favourable for increasing the neutral lipid accumulation in the stationary tumor cells, their RG and nuclei, as compared to exponentially growing cells. The sensitivity of tumor cells to peroxidation can be also enhanced with the help of exogenous polyunsaturated fatty acid (PUFA). Based on literature and our own data on Ehrlich ascites carcinoma (EAC), a working hypothesis is proposed to explain the enhanced selective sensitivity of tumor cells to PUFA peroxidation products (PP) suppressing the cell growth (especially in the stationary phase of EAC growth).

Ground-state correlation energies for two- to ten-electron atomic ions.

Improved estimates of the nonrelativistic stationary nucleus correlation energies of the ground-state atomic ions with three to ten electrons and Z up to 20 are derived by combining experimental data and improved ab initio calculations. Unlike previous work in this area, we focus on the correlation contribution to individual ionization energies, computed by comparing experimental data with relativistic complete-valence-space Hartree-Fock energies.

Are bound states of color-excited leptons responsible for anomalouse + e ? production in heavy ion collisions?

A model for the anomalouse+e− production in heavy ion collisions is proposed. The model is based on the hypothesis thate+e− production derives from the decay of “leptopions,” pionlike bound states of colored excitations ofe+ ande−. Order-of-magnitude estimates for the mass scale of the radial excitations and lifetime of the leptopion obtained by extrapolation from the case of the ordinary pion are in accordance with data. The model for leptopion production is based on the electromagnetic anomaly term. In the classical treatment of the nucleus-nucleus collision the leptopion production amplitude is essentially the Fourier transform of the scalar product of the electric field of the stationary target nucleus and the magnetic field of the colliding nucleus. The production amplitude becomes singular for certain values of the kinematical variables and in singularity the velocity of the leptopion is a definite function of the production angle measured with respect to the direction of the collision velocity. Due to the weak dependence of the velocity of the production angle in the forward direction the leptopions are apparently produced at rest in center-of-mass coordinates in accordance with the data. The observed peak ofe+e− production amplitude (in fact two peaks in some cases) is explained as a quantum diffraction effect resulting from the finite size of the colliding nuclei, when the collision velocity exceeds the velocity needed to overcome the Coulomb barrier. The production amplitude oscillates as a function of collision velocity and the period of oscillation is in accordance with the width of the observed velocity peak. In principle, several diffraction peaks are possible for elastic collisions in a plane, but the effects of strong interactions are expected to lead to the disappearence of the peaks at velocities larger than that needed to overcome the Coulomb barrier. An explanation for the unobservability of lepton color via strong interactions is proposed.

NMR study of one dimensional ionic conductor A xGa 8Ga 8+ xTi 16− xO 56 (ACs, Rb)

Ionic conduction in a new type of one-dimensional ionic conductor, A x Ga 8Ga 8+ x Ti 16− x O 56 (AGGTO), was investigated using NMR. Mobile 87Rb and 133Cs nuclei and stationary 69Ga and 71Ga nuclei in the framework were used as the probes. Temperature dependence of the line shape of 87Rb indicates that Rb + ions are in a motionally averaged state with the asymmetry parameter η of about 0.1 and the quadrupole coupling parameter ν Q of −8.6 MHz. The fact that T ∗ 1 of the mobile 133Cs and the stationary 71Ga nucleus show similar temperature dependences in the measured temperature range in CGGTO indicates that the Ga nuclei are good probes for observing ionic motion in the channel. The slope d( lnT 1 ∗)/ d(1/kT) in the high temperature limit gives E NMR = 0.06 eV, which is about one half of that in KAl-priderite. The smaller value ( E NMR = 0.03 eV) in RGGTO corresponds to the result of ac conductivity that RGGTO shows the highest conductivity in AGGTO.

Collision-induced intramultiplet mixing for Ne

We present an extension of the model-potential method of Ne/sup *//sup *//(2p)/sup 5/(3p)/-Ne collisions. The role of the electronic inversion symmetry in the core--valence-electron separation for stationary nuclei is examined. This leads to approximate electronic eigenfunctions and corresponding adiabatic potentials. In this, an essential element is the R-dependent mixing of gerade and ungerade core potentials, associated with the R-dependent uncertainty of the valence electron being located at the Ne/sup +/ ion or the Ne atom. Subsequently, nuclear dynamics is included in the approximate wave function and the role of the identity of the nuclei is considered. With the aim of testing our extended approximate treatment, we also present experimental /sup 20/Ne/sup *//sup */-Ne, and /sup 22/Ne/sup *//sup */-Ne total polarized cross sections Q/sub l//sub left-arrow//sub k//sup chemically bond//sup M//sup >//sup k/chemically bond$ for the /(2p)/sup 5/(3p)//sub k/ (or //alpha///sub k/..-->..//alpha///sub l/) transition, with M/sub k/ the magnetic quantum number of the electronic angular momentum J of the initial //alpha///sub k/ state with respect to the asymptotic relative velocity.