MHD instability at the cathode spot as the origin of the vortex formation in high-intensity plasma arcs

Magnetohydrodynamic instability in a high-intensity arc, similar to typical arcs in DC electric arc furnaces, is simulated using an induction based model under 2D axisymmetric conditions. Time-averaged results show a good agreement with steady-state calculated results expected for a stable arc. The transient results declare that z-pinch close to the cathode, occurring due to the high electrical current density, is responsible for arc instability in this region. The unstable behavior of the arc can be evaluated in a periodic procedure. Moreover, correlations between the fluctuations in total voltage drop curve and the arc shape are investigated: when the arc is in form of column (or bell) the total voltage drop is on a minimum peak; if there is an irregular expansion of the arc in form of arms, the total voltage drop shows a maximum peak.

Deterministic loading of a single strontium ion into a surface electrode trap using pulsed laser ablation

Trapped-ion quantum technologies have been developed for decades toward applications such as precision measurement, quantum communication and quantum computation. Coherent manipulation of ions' oscillatory motions in an ion trap is important for quantum information processing by ions, however, unwanted decoherence caused by fluctuating electric-field environment often hinders stable and high-fidelity operations.. One way to avoid this is to adopt pulsed laser ablation for ion loading, a loading method with significantly reduced pollution and heat production. Despite the usefulness of the ablation loading such as the compatibility with cryogenic environment, randomness of the number of loaded ions is still problematic in realistic applications where definite number of ions are preferably loaded with high probability. %The ablation loading is proven to be useful, being even compatible with cryogenic environment, except for the randomness of the number of loaded ions. In this paper, we demonstrate an efficient loading of a single strontium ion into a surface electrode trap generated by laser ablation and successive photoionization. The probability of single-ion loading into a surface electrode trap is measured to be 82\,\%, and such a deterministic single-ion loading allows for loading ions into the trap one-by-one. Our results open up a way to develop more functional ion-trap quantum devices by the clean, stable, and deterministic ion loading.

A critical discussion of different methods and models in Casimir effect

The Casimir-Lifshitz force acts between neutral material bodies and is due to the fluctuations (around zero) of the electrical polarizations of the bodies. This force is a macroscopic manifestation of the van der Waals forces between atoms and molecules. In addition to being of fundamental interest, the Casimir-Lifshitz force plays an important role in surface physics, nanotechnology and biophysics. There are two different approaches in the theory of this force. One is centered on the fluctuations inside the bodies, as the source of the fluctuational electromagnetic fields and forces. The second approach is based on finding the eigenmodes of the field, while the material bodies are assumed to be passive and non-fluctuating. In spite of the fact that both approaches have a long history, there are still some misconceptions in the literature. In particular, there are claims that (hypothetical) materials with a strictly real dielectric function $\varepsilon(\omega)$ can give rise to fluctuational Casimir-Lifshitz forces. We review and compare the two approaches, using the simple example of the force in the absence of retardation. We point out that also in the second (the "field-oriented") approach one cannot avoid introducing an infinitesimal imaginary part into the dielectric function, i.e. introducing some dissipation. Furthermore, we emphasize that the requirement of analyticity of $ \varepsilon(\omega)$ in the upper half of the complex $\omega$ plane is not the only one for a viable dielectric function. There are other requirements as well. In particular, models that use a strictly real $\varepsilon(\omega)$ (for all real positive $\omega)$ are inadmissible and lead to various contradictions and inconsistencies. Specifically, we present a critical discussion of the "dissipation-less plasma model". Our emphasis is not on the most recent developments in the field but on some conceptual, not fully resolved issues.

An analytical approximation to measure the extinction cross-section using: Localized Waves

We present a general expression for the optical theorem in terms of Localized Waves. This representation is well-known and commonly used to generate Frozen waves, Xwaves, and other propagation invariant beams. We analyze several examples using different input beam sources on a circular detector to measure the extinction cross-section.

Characterization of Orientation Correlation Kinetics: Chiral-mesophase Domains in Suspensions Charged DNA-rods

Bacteriophage DNA fd-rods are long and stiff rod-like particles which are known to exhibit a rich equilibrium phase behavior. Due to their helical molecular structure, they form the stable chiral nematic (N*) mesophases. Very little is known about the kinetics of forming various phases with orientations. The present study addresses the kinetics of chiral-mesophases and N*-phase, by using a novel image-time correlation technique. Instead of correlating time-lapsed real-space microscopy images, the corresponding Fourier images are shown for time-correlated averaged orientations. This allows to unambiguously distinguish to detect the temporal evolution of orientations on different length scales, such as domain sizes (depending on their relative orientations), and the chiral pitch within the domains. Kinetic features are qualitatively interpreted in terms of replica symmetry breaking of elastic deformations in the orthogonal directional axes of chiral-mesophase domains, as well by the average twist angle and the order parameter. This work can be interesting for characterizing other types of charged rods, mimicking super-cooled liquids and orientation glasses.

New physical parameterizations of monopole solutions in five-dimensional general relativity and the role of negative scalar field energy in vacuum solutions

Novel parameterizations are presented for monopole solutions to the static, spherically-symmetric vacuum field equations of five-dimensional general relativity. First proposed by Kaluza, 5D general relativity unites gravity and classical electromagnetism with a scalar field. These monopoles correspond to bodies carrying mass, electric charge, and scalar charge. The new parameterizations provide physical insight into the nature of electric charge and scalar field energy. The Reissner-Nordstr\"om limit is compared with alternate physical interpretations of the solution parameters. The new parameterizations explore the role of scalar field energy and the relation of electric charge to scalar charge. The Kaluza vacuum equations imply the scalar field energy density is the negative of the electric field energy density for all known solutions, so the total electric and scalar field energy of the monopole is zero. The vanishing of the total electric and scalar field energy density for vacuum solutions seems to imply the scalar field can be understood as a negative-energy foundation on which the electric field is built.

Critical behavior in the artificial axon

The Artificial Axon is a unique synthetic system, based on biomolecular components, which supports action potentials. Here we examine, experimentally and theoretically, the properties of the threshold for firing in this system. As in real neurons, this threshold corresponds to the critical point of a saddle-node bifurcation. We measure the delay time for firing as a function of the distance to threshold, recovering the expected scaling exponent of −1/2. We introduce a minimal model of the Morris-Lecar type, validate it on the experiments, and use it to extend analytical results obtained in the limit of ”fast” ion channel dynamics. In particular, we discuss the dependence of the firing threshold on the number of channels. The Artificial Axon is a simplified system, an Ur-neuron, relying on only one ion channel species for functioning. Nonetheless, universal properties such as the action potential behavior near threshold are the same as in real neurons. Thus we may think of the Artificial Axon as a cell-free breadboard for electrophysiology research.

On the derivation of a nonlinear generalized Langevin equation

We recast the Zwanzig's derivation of a non linear generalized Langevin equation (GLE) for a heavy particle interacting with a heat bath in a more general framework showing that it is necessary to readjust the Zwanzig's definitions of the kernel matrix and noise vector in the GLE in order to be able performing consistently the continuum limit. As shown by Zwanzig, the non linear feature of the resulting GLE is due to the non linear dependence of the equilibrium map by the heavy particle variables. Such an equilibrium map represents the global equilibrium configuration of the heat bath particles for a fixed (instantaneous) configuration of the system. Following the same derivation of the GLE, we show that a deeper investigation of the equilibrium map, considered in the Zwanzig's Hamiltonian, is necessary. Moreover, we discuss how to get an equilibrium map given a general interaction potential. Finally, we provide a renormalization procedure which allows to divide the dependence of the equilibrium map by coupling coefficient from the dependence by the system variables yielding a more rigorous mathematical structure of the non linear GLE.

Elastic behavior, pressure-induced doping and superconducting transition temperature of GdBa2Cu3O7-x

Doping superconductors are known to vary the superconducting transition temperature TC depending on the degree of holes or electrons introduced in a system. In this study, we report how pressure-induced hole doping influences the TC of GdBa2Cu3O7-x superconducting perovskite. The study was carried out in the framework of density functional theory (DFT) using the Quantum espresso code. Ultrasoft pseudopotential with generalized gradient approximation (GGA) and local density approximation (LDA) functional was used to calculate the ground state energy using the plane waves (PW). The stability criterion was satisfied from the calculated elastic constants. The BCS theory and the Mc Millan’s equation was used to calculate the TC of the material at different conditions of pressure. The underdoped regime where the holes were less than those at optimal doping was found to be below 20 GPa of doping pressure. Optimal doping where the material achieved the highest TC (max) ~ 20 GPa of the doping pressure. Beyond the pressure of ~20 GPa was the over doping regime where a decrease in TC was recorded. The highest calculated TC (max) was ~141.16 K. The results suggest that pressure of ~20 GPa gave rise to the highest TC in the study.

Unconventional non-Fermi liquid properties of two-channel Anderson impurities system

A theory for treating the unconventional non-Fermi liquid temperature dependence of physical quantities, such as the resistivity, in the Pr-based two-channel Anderson impurities system is developed. It is shown that their temperature dependences are essentially the same as those in the pure lattice system except for the case of extremely low concentration of Pr ions that is difficult to realize by the controlled experiments. This result is consistent with recent observations in diluted Pr-1-2-20 system Y1−xPrxIr2Zn20 (x = 0.024, 0.044, 0.085, and 0.44) reported in Yamane et al. Phys. Rev. Lett. 121, 077206 (2018), and is quite different from that in the case of single-channel Anderson impurities system in which the crossover between behaviors of the local Fermi liquid and heavy Fermi liquid occurs at around moderate concentration of impurities as observed in Ce-based heavy fermion system La1−xCexCu6.